Electroplating composition and method

ABSTRACT

Electroplating composition and method. In one embodiment, the composition comprises an electrolyte solution and an amine-based copolymer comprising monomer units of ethylene oxide and propylene oxide, with the propylene oxide present in a quantity of at least about 70 wt %. The method comprises electroplating a metal onto a substrate from the electroplating composition of the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject matter of this application relates to that of copending application Ser. No. 10/796,470, filed Mar. 9, 2004 for “Chemical structures and compositions of ECP additive to reduce pit defects”, which is assigned to a common assignee with this application. The disclosure of the copending application is incorporated herein by reference in their entirety.

BACKGROUND

The present invention relates in general to electroplating compositions and methods. More particularly, it relates to electroplating compositions and methods to deposit metals, particularly copper, on a substrate in the fabrication of semiconductor integrated circuits.

Due to the ever-decreasing size of semiconductor components and the ever-increasing density of integrated circuits on a wafer, the complexity of interconnecting the components in the circuits requires that the fabrication processes used to define the metal interconnects be subjected to precise dimensional control. Advances in lithography and masking techniques and dry etching processes, such as RIE (Reactive Ion Etching) and other plasma etching processes, allow production of conducting patterns with widths and spacings in the submicron range. Electrodeposition or electroplating has been identified as a promising technique for depositing conductive layers on substrates in the manufacture of integrated circuits and flat panel displays. Such electroplating processes have been used to achieve deposition of the copper or other metal layer with a smooth, level top surface. Consequently, much effort is currently focused on the design of electroplating hardware and chemistry to achieve high-quality films which are uniform across the entire surface of the substrates and which are capable of filling or conforming to very small device features. Copper has been found to be particularly advantageous as an electroplating metal.

Conventional electroplating techniques use copper sulfate (CuSO₄) for the main electrolyte in the electroplating bath solution. The solution may further include additives such as chloride ion and levelers, as well as accelerator and suppressors which increase and decrease, respectively, the rate of the electroplating process. The rate of deposition of copper on the substrate, and the quality and resulting electrical and mechanical properties of the metallization, are critically dependent on the concentration of these organic additives in the electroplating bath solution. One of the drawbacks of the conventional suppressors used in the electroplating bath solutions is that the suppressor causes poor wettability of the solution to the seed layer on a substrate, which in turn results in inadequate filling of the features.

An improved composition and method of electroplating with enhanced gap fill capability has been discussed in copending U.S. patent application Ser. No. 10/796,470, filed Mar. 9, 2004, the disclosure of which is incorporated herein by reference in its entirety. As discussed therein, a suppressor additive of EO-PO (ethylene oxide-propylene oxide) copolymer can be used to enhance the wetting of an electroplating bath solution on a metal seed layer, which results in uniform electroplating deposition and gap-filing with minimal tendency for immersion-related electroplating defects such as pits.

The solubility of the EO/PO copolymer in the plating solution is associated with the proportion of the two monomer units. In general, solubility increases with increased EO content due to higher hydrophilicity. Therefore, EO/PO copolymer with at least 40% EO content is typically used or the solubility is undesirably low. It has now been found, however, that the increased EO content decreases the ability to suppress copper deposition, especially on top of gap features. As a result, bottom or sidewall voids, or post CMP (chemical mechanical polish) pits can be observed. These problems are especially severe when filling gap features of 45 nm copper technology or below. It remains desirable to provide an improved suppressor that is readily soluble in the plating solution with suppression ability not compromised.

Note that the above description in deficiency of the existing suppressors merely shows a problem found by the inventors, not prior art for the purposes of determining the patentability of the present invention.

SUMMARY

According to one aspect of the invention, an electroplating composition is provided. In one embodiment, the electroplating composition comprises: an electrolyte solution; and an amine-based copolymer comprising monomer units of ethylene oxide and propylene oxide in the electrolyte solution, wherein the propylene oxide is present in the copolymer in a quantity of at least about 70 wt %.

In another embodiment, the electroplating composition comprises: an electrolyte solution; an amine-based copolymer comprising monomer units of ethylene oxide and propylene oxide in the electrolyte solution as a first suppressor additive, wherein the propylene oxide is present in the amine-based copolymer in a quantity of at least about 70 wt %; and a copolymer comprising monomer units of ethylene oxide and propylene oxide in the electrolyte solution as a second suppressor additive, wherein the ethylene oxide is present in the copolymer in a quantity of at least about 60 wt %.

According to another aspect of the invention, an electroplating method is provided. An exemplary method comprises: providing an electroplating bath comprising the above described electroplating composition; immersing a substrate in the electroplating bath; and electroplating metal onto the substrate from the electroplating composition.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference is made to a detailed description to be read in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic of an electrochemical plating system in implementation of the invention;

FIG. 2 is a cross section of a substrate with a metal layer electroplated thereon according to the composition and method of the invention; and

FIG. 3 is a flow diagram illustrating a typical flow of process steps according to the method of the invention.

DESCRIPTION

The invention has particularly beneficial utility in the electrochemical plating of copper on a semiconductor wafer substrate in the fabrication of semiconductor integrated circuits. The invention, however, is more generally applicable to the electrochemical plating of metals including but not limited to copper on substrates in a variety of industrial applications including but not limited to semiconductor fabrication.

The electroplating composition and method will be described here in greater detail. In the description, all percentages are by weight unless otherwise specified. Some embodiments of the invention, such as the exemplary embodiments described, may potentially achieve void-free filling down to 0.45 nm gap features where asymmetric or thin metal seed are typically found. In some embodiments, this can be accomplished by providing an amine-based EO-PO copolymer with high PO content as a suppressor additive, which provides strong suppression to prevent premature closing of the gap and the trapping of voids, with sufficient solubility in the plating bath.

Amine-based EO-PO copolymers have remarkable solubility (or cloud point) compared to general EO-PO copolymers. In general, the cloud point of EO-PO copolymer in 0.1% acid bath is less than 20° C. if the PO content is above 60%, while for amine-based copolymers, the cloud point can be higher than 80° C. even with 90% PO content. Accordingly, the amine-based copolymer used in the invention may comprise at least about 70% by weight propylene oxide (PO) with the solubility not compromised. Preferably, the amine-based copolymer comprises about 80-95% by weight propylene oxide (PO) and about 5-20% by weight ethylene oxide (EO). Although U.S. Pat. Nos. 6,531,046, 6,773,568, and U.S. Pat. No. 6,444,110 disclose polyoxyalkylene amine as suppressor additives, but the novel amine-based PO-EO copolymers and the PO content thereof are addressed.

Suitable amine-based EO-PO copolymers include but are not limited to those containing a core of alkylene diamine such as ethylene diamine, and those containing terminal alkyl amine such as lauryl amine or tallow amine. The copolymer may be a block, alternating, or random copolymer. A particularly preferred suppressor is EO-PO block copolymer of ethylene diamine (also known as poloxamine). Examples of commercially available EO-PO copolymer of ethylene diamine include SINOPOL TE series from Sino-Japan Chemical, Tetronic Series from BASF, and ADEKANOL TR series from Asahi Denka Kogyo. The suppressor preferably has a weight average molecular weight (Mw) of about 2,000-20,000, more preferably about 3,000-5,000.

In more preferred embodiments, an EO-PO copolymer with at least 60% EO content can be employed as a second suppressor. Although the high PO content suppressor improves gap-filling, it may reduce the interfacial tension of the electrolyte solution to about 30-40 dyne/cm². Lower interfacial tension increases the probability of bubble formation, which in turn, results in a series of pit defects that follow the wafer's arc of rotation during plating. Accordingly, an optional second suppressor with at least 60% EO content may be added to increase the interfacial tension to about 50-60 dyne/cm². The combination of these two suppressors may provide enhanced bottom-up fill ability while still providing high interfacial tension to optimize wetting on the seed surface to avoid pit defects.

The composition and method of the invention may be used with any formulation for the electroplating bath solution, such as copper, aluminum, nickel, chromium, zinc, tin, gold, silver, lead, or cadmium electroplating baths. The invention is also suitable for use with electroplating baths containing mixtures of metals to be plated onto a substrate. It is preferred that the electroplating bath be a copper alloy electroplating bath, and more preferably a copper electroplating bath. Typical copper electroplating bath formulations are well known to those skilled in the art and include, but are not limited to, an electrolyte and one or more sources of copper ions. Suitable electrolytes include sulfuric acid, acetic acid, fluoroboric acid, methane sulfonic acid, ethane sulfonic acid, p-toluenesulfonic acid, hydrochloric acid, phosphoric acid and the like. The acids are typically present in the bath in a concentration of about 1-300 g/L. The acids may further include a source of halide ions such as chloride ions. Suitable sources of copper ions include copper sulfate, copper chloride, copper acetate, copper nitrate, copper fluoroborate, copper methane sulfonate, copper phenyl sulfonate and copper p-toluene sulfonate. The copper ion sources are typically present in a concentration of about 10-300 g/L of electroplating solution.

In a preferred embodiment, the amine-based EO-PO copolymer with high PO content (as first suppressor additive) is present in the electrolyte solution in a concentration of about 100-300 ppm. The EO-PO copolymer with high EO content (as second suppressor additive) is present in the electrolyte solution in a concentration of about 50-100 ppm. An accelerator is typically present in the electrolyte bath solution in a concentration of about 2-50 ppm. The accelerator may be any type of commercially available accelerator known in the art for accelerating a metal electroplating deposition process.

Other electrochemical plating conditions suitable for implementation of the invention include a plating rpm of about 0-500 rpm; a plating current of about 0.2-20 mA/cm²; and a bath temperature of about 10-35° C. In addition, a leveling agent may be added to the electroplating bath solution at a concentration of about 5 mmol/L to 5 mol/L.

Referring to FIG. 1, an electrochemical plating (ECP) system suitable for implementation of the invention is shown. The system 10 may be conventional and includes a standard electroplating cell having an adjustable current source 12, a bath container 14, a copper anode and a cathode 18, which cathode 18 is the semiconductor wafer substrate to be electroplated with copper. The anode 16 and cathode/substrate 18 are connected to the current source 12 by wiring 38. The bath container holds an electrolyte bath solution 20. The system may further include a mechanism for rotating the substrate 18 in the bath 20 during the electroplating process, as is known by those skilled in the art.

The ECP system 10 may further include a pair of bypass filter conduits 24, a bypass pump/filter 30, and an electrolyte holding tank 34 for the introduction of additional electrolytes into the bath container, if necessary. The bypass filter conduits 24 typically extend through the anode 16 and open to the upper, oxidizing surface 22 of the anode at opposite ends of anode. The bypass filter conduits 24 connect to the bypass pump/filter 30 outside the bath container 14, and the bypass pump/filter 30 is further connected to the electrolyte holding tank 34 though a tank inlet line 32. The electrolyte holding tank 34 is, in turn, connected to the bath container 14 though a tank outlet line 36. It is understood that the ECP system described herein merely represents one example of a possible system for implementation of the invention, and other systems of alternative design may be used instead.

Referring to FIGS. 1-3, according to the method of the invention, a metal seed layer 19, such as copper, is deposited on a wafer substrate 18, as indicated in step S1 of FIG. 3. The metal seed layer 19 may be deposited using conventional chemical vapor deposition (CVD) or physical vapor deposition (PVD) techniques. The seed layer 19 typically has a thickness of about 50-1500 Å.

As indicated in step S2 of FIG. 3, the ECP electrolyte bath solution is prepared in the bath container 14. The electroplating bath solution 20 typically includes an accelerator and may include a leveling agent. Next, as indicated in step S3, the amine-based EO-PO copolymer with high PO content (≧70%) and optionally a EO-PO copolymer with high EO content (≧60%) as suppressor additive(s) are mixed with the electroplating bath 20. The anode 16 and substrate 18 are then immersed in the bath solution 20 and connected to the adjustable current source 12 through wiring 38.

As indicated in step S4 of FIG. 3, the cathode/substrate 18 is immersed in the bath solution 20. The entire surface of the seed layer 19, as well as gap features on the substrate 18, are thoroughly wetted by the bath solution 20. As shown in FIG. 2 and step S5 of FIG. 3, a metal layer 21 is electroplated onto the seed layer 19, typically as follows. The electroplating bath 20 is heated to a temperature typically from about 10° C. to 35° C. In operation of the ECP system 10, the current source 12 applies a selected voltage potential, typically at room temperature, between the anode 16 and the cathode/substrate 18. This voltage potential creates a magnetic field around the anode 16 and the cathode/substrate 18, affecting the distribution of the copper ions in the bath solution 20. typically, a voltage potential of about 2 volts may be applied for about 2 minutes, and a plating current of about 0.2-20 mA/cm² flows between the anode 16 and the cathode/substrate 18. The plating rpm for the substrate 18 is typically about 0-500 rpm. Consequently, copper is oxidized at the oxidizing surface 22 of the anode as ionic copper is reduced to form copper deposit at the interface between the cathode/substrate 18 and the copper sulfate bath.

Due to the improved bottom-up fill ability and the thorough and uniform wetting of the electrolyte bath solution, the electroplated metal layer 21 is substantially continuous and free of structural deformities such as voids or pits. Experimental results indicate that the novel amine-based suppressor additive achieved void-free filling in gap features as small as 45 nm. Accordingly, the electroplating composition and method is particularly effective in high aspect ratio gap-filling applications.

While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

1. An electroplating composition, comprising: an electrolyte solution; and an amine-based copolymer comprising monomer units of ethylene oxide and propylene oxide in the electrolyte solution, wherein the propylene oxide is present in the copolymer in a quantity of at least about 70 wt %.
 2. The electroplating composition of claim 1, wherein the propylene oxide is present in the copolymer in a quantity of about 80-95 wt %.
 3. The electroplating composition of claim 1, wherein the amine-based copolymer has a cloud point temperature of above 80° C. in 0.1% acid solution.
 4. The electroplating composition of claim 1, wherein the amine-based copolymer comprises a core of alkylene diamine.
 5. The electroplating composition of claim 4, wherein the amine-based copolymer comprises an ethylene oxide-propylene oxide (EO-PO) copolymer of ethylene diamine.
 6. The electroplating composition of claim 1, wherein the amine-based copolymer comprises terminal alkyl amine.
 7. The electroplating composition of claim 6, wherein the amine-based copolymer comprises an ethylene oxide-propylene oxide (EO-PO) copolymer of lauryl amine or tallow amine.
 8. The electroplating composition of claim 1, wherein the amine-based copolymer has a weight average molecular weight (Mw) of about 2,000-20,000.
 9. The electroplating composition of claim 1, wherein the amine-based copolymer is a block copolymer.
 10. The electroplating composition of claim 1, wherein the amine-based copolymer is a random copolymer.
 11. The electroplating composition of claim 1, wherein the amine-based copolymer is an alternating copolymer.
 12. The electroplating composition of claim 1, wherein the amine-based copolymer is present in the electrolyte solution in a concentration of about 100-300 ppm.
 13. An electroplating composition, comprising: an electrolyte solution; an amine-based copolymer comprising monomer units of ethylene oxide and propylene oxide in the electrolyte solution as a first suppressor additive, wherein the propylene oxide is present in the amine-based copolymer in a quantity of at least about 70 wt %; and a copolymer comprising monomer units of ethylene oxide and propylene oxide in the electrolyte solution as a second suppressor additive, wherein the ethylene oxide is present in the copolymer in a quantity of at least about 60 wt %.
 14. The electroplating composition of claim 13, wherein the first and second suppressor additives are present in the electrolyte solution in concentrations of about 100-300 ppm and 50-100 ppm, respectively.
 15. The electroplating composition of claim 13, wherein the second suppressor is a random copolymer.
 16. The electroplating composition of claim 13, wherein the second suppressor is a block copolymer.
 17. The electroplating composition of claim 13, wherein the second suppressor is an alternating copolymer.
 18. The electroplating composition of claim 13, wherein the amine-based copolymer comprises terminal alkyl amine.
 19. A method of electroplating a metal on a substrate, comprising: providing an electroplating bath comprising the electroplating composition of claim 1; immersing the substrate in the electroplating bath; and electroplating the metal onto the substrate from the electroplating composition of claim
 1. 20. The method of claim 19, wherein the electroplating composition further comprises an ethylene oxide-propylene oxide (EO-PO) copolymer, wherein the ethylene oxide is present in the copolymer in a quantity of at least about 60 wt %.
 21. The method of claim 19, wherein the substrate is a semiconductor wafer substrate. 